A standardized mechanical interface (SMIF) system has been proposed to reduce particle contamination by significantly reducing particle fluxes onto wafers. This end is accomplished by mechanically insuring that during transport, storage and processing of the wafers, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by insuring that particles from the outside environment do not enter the immediate internal wafer environment.
The SMIF concept is based on the realization that a small volume of still, particle free air, with no internal source of particles, is the cleanest possible environment for wafers. Further details of one proposed system are described in the article "SMIF: A Technology for Wafer Cassette Transfer and VLSI Manufacturing", by Mihir Parikh and Ulrich Kaemph, Solid State Technology, July 1984, pp. 111-115, and the above cross-referenced applications.
The proposed SMIF system has three main components, namely, (1) minimum volume, dust proof transportable containers or boxes are used for storing and transporting wafer cassettes; (2) canopies are placed over the cassette ports of processing equipment so that the environments inside the boxes and the canopies become miniature clean spaces; and (3) doors on the boxes are designed to mate with doors on the interface ports on the equipment canopies and two doors are open simultaneously so that particles which may have been on the external door surfaces are trapped (sandwiched) between the doors
In the proposed SMIF system, a box is placed at the interface port on top of the canopy at a desired processing station; latches release the boxed door and the interface port door simultaneously A mechanical elevator lowers the two doors with the cassette riding on top into the canopy covered space. A manipulator picks up the cassette and places into the cassette port/elevator of the equipment. After processing, the reverse operation takes place.
In typical processing environments today, "clean rooms" are established in which through filtering and other techniques attempts are made to remove particles which may cause contamination on semiconductor wafer surfaces. The SMIF concept is one way which has come under consideration for improving the processing environment over that available in clean rooms.
The proposed SMIF systems involve transporting cassettes of wafers from processing station to processing station inside the boxes. A given processing station may be located long distances from the preceding station. Further, the processing may be complex, involving a large number of steps different processing times, requiring the boxes including wafer cassettes to be stored between processing stations. Thus there is a need to identify the boxes containing wafers so that information about the wafers within the boxes can be processed.
The proposed SMIF systems, however, have not been fully satisfactory. The SMIF systems which have been proposed include boxes which may be marked with "OCR" or bar codes. This sort of proposed marking will identify the particular box, however, the user is unable to effectively include information with the box concerning the wafers within the box. Accordingly, there is a need for improved apparatus for information processing in SMIF systems.